Joint IP/optical layer restoration after a router failure

ABSTRACT

A method and system for providing joint IP/Optical Layer restoration mechanisms for the IP over Optical Layer architecture, particularly for protecting against router failure within such architecture, includes any one of plural node elements participating in the detection and restoration of the joint IP/Optical Layer architecture upon the failure of a router in one of the nodes. The plural node elements may include, but are not limited to, one of plural routers and an optical cross-connect.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/908,752,filed Jul. 20, 2001.

FIELD OF THE INVENTION

The invention generally relates to optical communications andparticularly a method for the restoration of a joint IP/optical layerafter failure of a router therein.

BACKGROUND OF THE INVENTION

With the Internet rapidly replacing traditional telephone networks asthe ubiquitous network infrastructure, there is ever-increasing consumerdemand for greater bandwidth, which translates to a need for increasedsystem performance. Coping with the continuing high growth rate ofInternet traffic volume is a significantly challenging scalabilityproblem. Fiber optics using Wavelength Division Multiplexing (WDM)offers the enormous capacity that the Internet requires to continue togrow at its present and projected future rates. In addition, theincreasing agility of the latest Optical Layer Cross-Connects (OLXCs)offers the ability to dynamically change the optical layer connectivityon small time scales. OLXCs have the ability to convert the wavelengthof any incoming channel to any outgoing wavelength (i.e. have wavelengthconversion).

Internet Protocol (IP) network connectivity is more often being providedby optical circuits, including OC-48/192, for example. Thus, FIG. 1( a)is a schematic diagram showing the connectivity of IP layer 5 to anoptical layer 10. FIG. 1( b) shows a more specific schematic diagram inwhich IP router 15 may be either hard-wired to Dense Wave DivisionMultiplexer (DWDM) 20 for transport, or it may be connected to OLXC 25.

There is an underlying conflict, however, between the typical datagram(connectionless) service that supports the best-effort data delivery ofthe Internet and virtual circuit (connection-based) service. Thisconflict is exacerbated in the world of optical networks, due to thefixed nature of the wavelengths available and the restoration of servicein optical networks.

Optical networks are connection oriented and designed for fixed rate bitstreaming with very low error rates. Whereas the Internet employs softstate where possible, the state of the optical infrastructure that isencoded in its OLXCs is hard and must be explicitly removed. The keyelements in the success of the Internet have been its simplicity and theflexibility of the Internet service model, and therefore a significantchallenge in leveraging the new optical capabilities to enhance theInternet and other services is to manage the optical resourcesefficiently, without sacrificing the simplicity and flexibility of theInternet.

In spite of most traffic and media types becoming internet protocol (IP)based, multiple-hop high-bandwidth optical connections referred to aslightpaths will continue to be of value. Aggregate loads between majormetropolitan areas are rather stable, with most of the achievablestatistical multiplexing already attained in the regional and collection(distribution) portion of the network. With electronic switching systemscoping with substantial regional network volumes, this load canconveniently be assigned to point-to-point lightpaths that bypassintermediate backbone routers, reducing their load and reducingend-to-end delay and delay variation. Traffic engineering, i.e., loadand quality management, is increasingly performed by adjustingconnectivity and capacity between major backbone gateways on arelatively large time-scale, still small compared to the time-scale ofprovisioning.

This is both a primary function of, and a significant reason that, ATMor Multi-Protocol Label Switching (MPLS) is employed below the IP layerby most network operators. Agile, dynamically configurable OLXCs allowthe use of the optical layer directly to implement these functions,avoiding having ATM or MPLS as intermediate layers in future networks.Lightpaths carrying transit traffic, or non-IP traffic, may remain asignificant source of revenue for network operators for the foreseeablefuture. Whereas much of the transit capacity may carry IP traffic,operators leasing optical capacity may choose not to disclose this.

There are issues involving networks in general as they relate to whereparticular service and intelligence are provided. Functions previouslyprovided by a SONET/SDH layer.

SONET (Synchronous Optical NETwork)/SDH (Synchronous Digital Hierachy)is an industry standard for broadband optical fiber communications. Itprovides universal optical interfaces at OC-N/STM-M rate. It alsoprovides integrated OAM&P capabilities within each network element whichenables fast protection/restoration. A good reference book is“Understanding SONET/SDH, Standards and Applications” by Ming-ChwanChow, Andan Publisher, 1995.) interposed (not shown) above optical layer10 must be distributed between IP layer 5 and Optical Layer 10 in thearchitecture of FIGS. 1( a) and 1(b), including the recovery of serviceafter equipment failure.

Restoration may be provided by either the IP layer or the optical layer10. The optical layer 10 is able to independently provide sub-secondprotection and/or restoration for link failures, that is when a fiber iscut, and is the most cost-effective solution therefore. However, when arouter in the IP/Optical Layer architecture fails, the optical layer hasno independent awareness of the router failure.

Thus, presently, it is the IP layer 5 that includes the necessaryfunctionality for protecting against router failure. In addition, the IPlayer 5 may include extra link capacity so that the quality of servicemay be preserved in the event of a router failure. As a result, it isthen more cost-effective to use the extra link capacity to protectagainst link failure, and thus there is no incentive to utilize theprotection/restoration function provided by the optical layer 10.Accordingly, IP network operators may choose a restoration strategy thatdepends solely upon the IP layer 5.

However IP layer restoration systems have some disadvantages. Forinstance, the failure of an unprotected link may result in amean-time-to-repair in the range of four to ten hours althoughmean-time-to-repair for a router failure may be less than one hour.Still, the excessive amount of down-time due to a link failure mayresult in further router failures, which has the potential forsignificant network congestion.

SUMMARY OF THE INVENTION

Accordingly, the present invention includes a method and system forproviding joint IP/Optical Layer restoration mechanisms for the IP overOptical Layer architecture, particularly for protecting against routerfailure within such architecture.

According to an example embodiment of the present invention, any one ofplural node elements may participate in the detection and restoration ofthe joint IP/Optical Layer architecture upon the failure of a router inone of the nodes. The plural node elements may include, but are notlimited to, one of plural routers and an optical cross-connect (OXLC).

For example, a node element may detect a failure in a lightpath to anode, transmit a request to an optical network to re-establish thelightpath, and reestablish the lightpath using a backup or redundantrouter in place of a failed router at the same node thereof.

All routers at the nodes are used during normal operations, though, forthe purposes of this description, one router may be deemed to be“redundant” since it backs up traffic for another router that has failedat the same node. The node element that detects the failed router mayinclude a router, disposed at another node, whereby the lightpath runsbetween the detecting router and the failed router; a redundant routerat the same node as the failed router; or an OXC at the same node as thefailed router.

If the router failure is detected by a router, at either a remote nodeor at the same node as the failed router, the detecting router transmitsa request to an OXC at the respective node that the lightpath bere-established using the redundant router in place of the failed router.If the detecting router is at the remote node, the OXC at the remotenode transmits the request to the OXC at the same node as the failedrouter.

Upon receiving the request for re-establishing the failed lightpath byusing the redundant router in place of the failed router, the OXC at thesame node as the failed router coordinates the re-establishment of alllinks using the redundant router in place of the failed router. Also,the OXC at the same node as the failed router may also detect the failedrouter and re-establish links using the redundant router in place of thefailed router.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) shows a schematic diagram of a joint IP/Optical Layerarchitecture.

FIG. 1( b) shows a more detailed schematic diagram of a joint IP/Opticallayer architecture, including the interconnection options therefore.

FIG. 2 shows an example IP architecture, as part of an exampleembodiment of the present invention, in which a router has failed.

FIG. 3 shows an example of the IP over Optical Layer architecture,according to an example embodiment of the present invention, in which arouter has failed.

FIG. 4 shows an example IP architecture, as part of an exampleembodiment of the present invention, in which a path has been re-routedafter a router has failed.

FIG. 5 is a flow chart showing an example method embodiment according tothe present invention for a router at a remote node.

FIG. 6 is a flow chart showing an example method embodiment according tothe present invention for a router at a home node.

FIG. 7 is a flow chart showing an example method embodiment according tothe present invention for an optical cross-connect at a home node.

DETAILED DESCRIPTION OF THE INVENTION

As set forth above, FIG. 1( b) illustrates a joint IP/Optical Layernetwork node with the optical layer cross-connect (OLXC) 25 connected toDWDM 20, to thereby be connected to other OLXCs. The network node mayfurther include IP router 15, along with dynamically-reconfigurable OLXC25. Optical lightpaths may be established between network elements, viaOLXCs, and the lightpaths serve as a virtual circuit.

In order to facilitate the description of the present invention thefollowing network objects are defined.

A Wavelength Division Multiplexer (WDM) is a system that convertsmultiple optical inputs into narrowly spaced wavelength optical signalswithin an optical amplification band and couples them onto a singlefiber. At the receiving end, the amplified signal may be de-multiplexedand converted to multiple channels of standard wavelength to interfacewith other equipment. It may also be possible to take the wavelengthspecific signals directly as the inputs. In that case, no wavelengthconversion may be necessary at the WDM system. The WDM system may or maynot be integrated with an OLXC.

A channel is a unidirectional optical tributary connecting two OLXCs.Multiple channels may be multiplexed optically at the WDM system. Onedirection of an OC-48/192 connecting two immediately neighboring OLXCsis an example of a channel. A single direction of an Optical channel(Och) as defined in ITU-T G.872 between two OLXCs over a WDM system isanother example of a channel. A channel may generally be associated witha specific wavelength in the WDM system. However, in a WDM system withtransponders, the interfaces to the OLXC may be a standard single color(1310 or 1550 nm). Further, a single wavelength may transport multiplechannels multiplexed in the time domain. For example, an OC-192 signalon a fiber may carry four STS-48 channels. For these reasons, a channelmay be defined separately from wavelength although in most applicationsthere is a one-to-one correspondence.

An optical layer cross-connect (OLXC) is a switching element thatconnects an optical channel from an input port to an output port. AnOLXC may also be referred to as an optical cross-connect (OXC), andtherefore shall be referred to as “OXC” hereafter.

A drop port is an OXC port that connects to the end client networkelement (NE). The drop interface may connect the client port to the OXCdrop port. The OXC drop port is essentially a User Network Interface(UNI) that connects end devices to the optical layer. The drop portterminates the user network interface between the client NE and theoptical network. It is necessary to distinguish this type of interfacefrom others to identify network requests originating from a client NE.

A network port is an OXC port that does not directly interface with anend client NE. A Network Port in an OXC interfaces with another NetworkPort via a WDM system or directly via optical fibers.

A lightpath is an abstraction of optical layer connectivity between twoend points. A lightpath is a fixed bandwidth connection (e.g. onedirection of a STM-N/OC-M payload or an Och payload) between two networkelements (NEs) established via OXCs. A bidirectional lightpath includestwo associated lightpaths in opposite directions routed over a same setof nodes.

A source may be a client router physically connected to an OXC by one ormore OC-48/192 interfaces. A source may also be a non-IP NE connected tothe OLXC via an OC-48/192 interface. In the case of an IP router source,the router may have an IP address, and the physical interfaces to theOXC are identified with some set of addresses (potentially a single IPaddress or a unique address per port). In the case of a non-IP NE,either the NE may be assigned an IP address, or the OLXC port connectingthe NE may have an IP address. For non-IP aware equipment interfacingthe OLXC, any connection request must be originated externally via aproxy or external OS interfaces. The destination is essentially the sameas the source from the physical interface perspective. When a request isgenerated from one end, the other end client or end OXC interface maybecome the destination.

A prominent feature of joint IP/Optical Layer network architectureaccording to an example embodiment of the present invention is thatevery office or node, A-F, in the network includes multiple, orredundant, IP routers 100 _(A)-100 _(F). and a dynamicallyreconfigurable OXC 200 _(A)-200 _(N), as shown in FIG. 3, although thepresent invention is in no way limited thereto. In FIG. 3, however, onlyoffice/node B is shown as having multiple routers 100 _(B1)-100 _(B2),though the present invention is not limited thereto. Rather, it isintended, in the present example embodiment of the invention, that alloffices/nodes have multiple, or redundant, IP routers 100 _(N).

Each IP office/node may be connected to other offices/nodes by one ormore lightpaths. On each link within the network, one channel/wavelengthis assigned as the default routed (one hop) lightpath. The routedlightpath may provide router-to-router connectivity over this link.These routed lightpaths may reflect (and are thus identical to) thephysical topology. The assignment of this default lightpath is byconvention, e.g. the “first” channel/wavelength. All traffic using thislightpath is IP traffic and is forwarded by the router.

As shown in FIG. 3, IP routers 100 _(N) at the respective offices/nodesmay communicate with their respective OXCs 200 _(N) through a logicalinterface (not shown). The logical interface defines a set of basicprimitives to configure the respective OXC 200 _(N), and to enable therespective OXC 200 _(N) to convey information to the respective router100 _(N). The mediation device translates the logical primitives to andfrom the proprietary controls of the OXC. A further embodiment mayintegrate the routers and their respective OXC into a single box orcomponent and use a proprietary interface implementation, while stillproviding equivalent functionality to the interface described herein.

Beyond the node local mechanisms, signaling mechanisms may be requiredto construct optical lightpaths. An Application Programming Interface(API) call to create a path may require at least five parametersincluding: destination, wavelength, bandwidth, restoration flag, and atransparency flag. If the restoration flag is set, the lightpath will beprotected. Lightpaths without the transparency flag are assumed to carryIP services, and may be rerouted if needed. On completion, an explicittear down message is sent to remove the path.

Lightpath services may include lightpath requests between a source anddestination, such as an API call with the following attributes:

As set forth above, restoration could be done at the IP layer 5 and/orthe Optical Layer 10, as shown in FIG. 1( a). The present invention willbe explained in the exemplary context of an ISP central office, usingthe schematic diagrams of FIGS. 2-4. The IP network of FIG. 2 includes,at each node therein, at least 2 backbone routers for redundancy, thoughthe detailed office architecture is shown for office B only. Theserouters, 100 _(N), aggregate all traffic to or from routers that connectto the customers of the IP network.

Under current IP routing systems, for example, when router 100 _(B1) atoffice/node B fails, IP traffic from office 100 _(A) to 100 _(B) wouldgo around offices 100 _(D), 100 _(E), 100 _(F), and 100 _(C) to reachoffice 100 _(B) via router 100 _(B2), the backup router for 100 _(B1).Similarly, traffic from office 100 _(A) to 100 _(C), which originallywent through office 100 _(B) would need to go around offices 100 _(D),100 _(E), 100 _(F), and 100 _(C) to reach 100 _(C). Additional capacitymay therefore be needed on all the inter-office links.

Under current IP rerouting systems, for example, when router 100 _(B),at office/node B fails, IP traffic from office 100 _(A) to 100 _(B)would go around offices 100 _(D), 100 _(E), 100 _(F), and 100 _(C) toreach office 100 _(B) via router 100 _(B2), the backup router for 100_(B1). Similarly, traffic from office 100 _(A) to office 100 _(C), whichoriginally went through office 100 _(B) would need to go around offices100 _(D), 100 _(E), 100 _(F), and 100 _(C) to reach office 100 _(C).Additional capacity may therefore be needed on all the inter-officelinks.

With the new IP over Optical Layer architecture shown in FIG. 3,according to an embodiment of the present invention, each office/nodemay be equipped with one OXC 200 _(N), which connects to the twobackbone routers 100 _(N1) and 100 _(N2) at the same office/node. Thenall the OXCs 200 _(N) may be connected by a mesh topology. Links betweenrouters are provided by direct lightpaths through the Optical Layer 10,which includes OXC's 200 _(N). In FIG. 3 solid lines represent physicallayer connectivity, and the dotted lines show the OC-48 links that maybe used for the transport of packets between the routers at offices 100_(N) and to the neighboring offices.

In the restoration scheme according to an embodiment of the presentinvention, when router 100 _(B1) at office B fails, bringing down bothinter-office lightpath link between routers 100 _(A) and 100 _(B1) andthe lightpath link between routers 100 _(B1) and 100 _(B2), router 100_(A) may detect that router 100 _(B1) has failed and may request a newconnection to be set up to the backup router, R_(B2). Further, OXC_(B)that connects to failed router 100 _(B1) directly may detect the failureand coordinate the setup of the new lightpath link between routers 100_(A) and 100 _(B2). This new link may use the same port for the failedlink between routers 100 _(A) and 100 _(B1) on router 100 _(A), andeither the same port for the failed lightpath link between routers 100_(B1) and 100 _(B2) on router 100 _(B2), or a spare port on router 100_(B2). In addition, the bandwidth originally used for the lightpath linkbetween routers 100 _(A) and 100 _(B1) may be reused, as may theintra-office cabling from router 100 _(A) to OXC_(A) and the cablingfrom OXC_(B) to 100 _(B2). The restoration for router failures,described above, is implemented in a time period of a couple of seconds.

More specifically, as shown in FIG. 5, the failure of router 100 _(B1)at office/node B (step 500) may be detected by router 100 _(A) atoffice/node A, as in step 505. In step 510, router 100 _(A) may send arequest to OXC_(A), also at node A, to restore the link between routers100 _(A) and 100 _(B1) by setting up a new link (i.e., lightpath)between router 100 _(A) and 100 _(B2). The signaling mechanism in theoptical layer coordinates the lightpath establishment. The request maybe transmitted from OXC_(A) to other OXC's that are on the newlightpath, i.e., OXC_(B) in this case in step 515, and may complete allnecessary switching in OXC_(A) to OXC_(B) to establish the newlightpath. Then, in step 525, upon restoration of the lightpath links tooffice/node B, routing in the IP layer will automatically discover thenew link between 100 _(A) and 100 _(B2), and router 100 _(B1) may bereplaced by router 100 _(B2) for all IP traffic through office/node B,and restoration may be complete at step 530.

The failure of router 100 _(B1), at step 600, may also be detected bythe redundant router 100 _(B2), which is at the same node as the failedrouter, at step 605, as depicted in the flowchart in FIG. 6. In step610, router 100 _(B2) sends a request to OXC_(B) that it connects todirectly, also at node B, to restore the connection to office A bysetting up a new lightpath link to routers 100 _(A). In step 615, thesignaling mechanism may forward the request from OXC_(B) to OXC_(A) tocomplete all necessary switching to establish the new lightpath. Then,in step 620, upon restoration of the lightpath link to office/node A,routing in the IP layer will may automatically discover the new linkbetween 100 _(A) and 100 _(B2), and router 100 _(B1) will be replaced byrouter 100 _(B2) for all IP traffic through office/node B, andrestoration may be complete at step 625.

Further, as shown in the flowchart of FIG. 7, the failure of router 100_(B1), at step 700, may be detected by the cross-connect OXC_(B), whichis disposed at the same office/node B as the failed router 100 _(B1) asin step 705. Since OXC_(B) controls connections for all routers at nodeB, in step 710, OXC_(B) may restore all inter-office links associatedwith failed router 100 _(B1) with router 100 _(B2) via the signalingmechanisms, thus ending restoration at step 715.

The IP layer topology resulting from the restoration described inaccordance with the example method embodiments of FIGS. 5-7 above isshown in FIG. 4. As a result of the restoration implementation describedabove, lightpath traffic, as shown in FIG. 4, may utilize lightpath linkfrom router 100 _(A) to router 100 _(B2) using the same number of hopswith no additional backbone capacity required.

As set forth above, intra-office capacity from cross-connect OXC_(B) torouter 100 _(B2), for example, that was formerly used for theintra-office link between routers 100 _(B1) and 100 _(B2) may be reused.Both intra-office lightpath links may require the same amount ofadditional intra-office capacity from the backup router 100 _(B2) to allprovider edge routers. With the restoration scheme described above,lightpath traffic between router 100 _(A) and router 100 _(C), viarouter 100 _(B), now may use the new link between router 100 _(A) androuter 100 _(B2), with one intra-office hop less than an original pathto go across office B and with no additional backbone capacity required.In comparison, IP rerouting would send the traffic via another route,thus potentially requiring additional backbone link capacity and verylikely increasing the hop count.

Thus, in this example restoration against the failure of router 100_(B1) has been achieved with no requirement for additional backbonebandwidth, OXC ports, or router ports.

In other cases with different topology, additional ports may be requiredon the backup router. For example, if one more backbone link is added torouter 100 _(B1) in the original network shown in FIG. 2, for example alightpath link between routers 100 _(E) and 100 _(B1), in addition torestoring the lightpath link between routers 100 _(A) and 100 _(B1)using the new lightpath link between routers 100 _(A) and 100 _(B2), thelightpath link between routers 100 _(E) and 100 _(B1) may be replaced bynew lightpath link between routers 100 _(E) and 100 _(B2). Since thereis only one port on router 100 _(B2), e.g., the port used by the failedintra-office lightpath link between routers 100 _(B) and 100 _(B2),reusable taken by the lightpath link between routers 100 _(A) and 100_(B2), an port may be required on router 100 _(B2) for the furtherrequired lightpath link between routers 100 _(E) and 100 _(B2). Ingeneral, the minimum number of additional ports needed on the backuprouter equals the total number of inter-office links on the failedrouter reduced by the number of re-usable ports (i.e., same type ofports) on the backup router that can be used by the failed intra-officelinks between the failed router and its backup router.

After a router failure is repaired, it is desirable to revert back tothe normal connections. We describe the details in the following threecases:

No re-use of the wavelength(s) and port(s) of the replaced lightpath

When a neighbor of the failed router detects that the failure has beenrepaired, it may first request the replaced lightpath to bere-established using the original wavelength(s) and port(s). After theoriginal lightpath has been restored, it may then request the recoverylightpath to be torn down. This case results in minimum interruption ofthe traffic.

Re-use of the wavelength(s) without the re-use of the port(s) of thereplaced lightpath

When a neighbor of the failed router detects that the failure has beenrepaired, it may first request the replaced lightpath to bere-established using the original port(s) and new wavelength(s) iffeasible. After the replaced lightpath has been restored, it may thenrequest the recovery lightpath to be torn down. However, if additionalwavelength(s) are not available or if it is required to revert back tothe same wavelength(s) as the one(s) used in the normal condition, therecovery lightpath may need to be torn down first before the originalone gets restored using the original port(s) and wavelength(s). This mayresult in some traffic loss during the reversion process.

Re-use of the wavelength(s) or port(s) of the replaced lightpath

When a neighbor of the failed router detects that the failure has beenrepaired, it may first request the replaced lightpath to bere-established using new port(s) and wavelength(s) if feasible. Afterthe replaced lightpath has been restored, it may then request therecovery lightpath to be torn down. However, if additional wavelength(s)or port(s) is not available or if it is required to revert back to thesame port(s) and wavelength(s) as the ones used in the normal condition,the recovery lightpath needs to be torn down first before the originalone gets restored using the original port(s) and wavelength(s). This mayresult in some traffic loss during the reversion process.

Note that the restoration mechanisms proposed here are applicable tofailure restoration for router interfaces. It is also applicable tocases without backup routers in the same office. Instead, a router in aneighboring office can be used as the backup router.

While the invention has been described with respect to specific examplesincluding presently preferred modes of carrying out the invention, thoseskilled in the art will appreciate that there are numerous variationsand permutations of the above described systems and techniques that fallwithin the spirit and scope of the invention as set forth in theappended claims.

1. A method of restoring an IP/Optical Layer after failure of an IProuter for routing IP packets between nodes, said method comprising thesteps of: detecting an IP router connectivity failure in a signal pathto a first node; transmitting a request to an optical network tore-establish the connectivity; and reestablishing the failed signal pathusing a redundant IP router in place of the failed IP router.
 2. Themethod of claim 1, wherein the path is a light path between the firstnode and a second node.
 3. The method of claim 2, wherein the failure inthe signal path to the other of the plurality of nodes is detected by anIP router at a second node, and wherein the failed IP router and theredundant IP router are at the first node.
 4. The method of claim 2,wherein the failure in the signal path to the other of the plurality ofnodes is detected by the redundant IP router at the first node, andwherein the failed IP router is at the first node.
 5. The method ofclaim 2, wherein the failure in the signal path to the first node isdetected by an optical cross-connect at the first node, and wherein thefailed IP router and the redundant IP router are at the first node. 6.The method of claim 3, wherein said transmitting step includes the IProuter at the second node transmitting the request to an opticalcross-connect at the second node to reestablish the signal path to thefirst node by using the redundant IP router in place of the failed IProuter.
 7. The method of claim 6, wherein said transmitting step furtherincludes the optical cross-connect at the second node transmitting therequest to an optical cross-connect at the first node.
 8. The method ofclaim 4, wherein said transmitting step includes the redundant IP routertransmitting the request to an optical cross-connect at the first nodeto re-establish the signal path by using the redundant IP router inplace of the failed IP router.
 9. The method of claim 5, wherein saidtransmitting step includes the optical cross-connect at the first nodetransmitting the request to an optical cross-connect at another node tore-establish the signal path by using the redundant IP router in placeof the failed IP router at the first node.
 10. A computer-readablemedium at a node method of an IP/Optical Layer, said computer-readablemedium having computer-executable instructions for performing, afterfailure of an IP router in one of a plurality of nodes, the steps of:detecting a failure in a signal path to a first node; transmitting arequest to an optical network to re-establish the signal path; andreestablishing the failed signal path using a redundant IP router inplace of a failed IP router.
 11. The computer-readable medium havingcomputer-executable instructions according to claim 10, wherein thesignal path is a light path between the first node and a second node.12. The computer-readable medium having computer-executable instructionsaccording to claim 11, wherein the failure in the signal path to theother of the plurality of nodes is detected at an IP router at a secondnode, and wherein the failed IP router and the redundant IP router areat the first node.
 13. The computer-readable medium havingcomputer-executable instructions according to claim 11, wherein thefailure in the signal path to the other of the plurality of nodes isdetected at the redundant IP router at the first node, and wherein thefailed IP router is at the first node.
 14. The computer-readable mediumhaving computer-executable instructions according to claim 11, whereinthe failure in the signal path to the first node is detected by anoptical cross-connect at the first node, and wherein the failed IProuter and the redundant IP router are at the first node.
 15. Thecomputer-readable medium having computer-executable instructionsaccording to claim 12, wherein said transmitting step includes the IProuter at the second node transmitting the request to an opticalcross-connect at the second node to re-establish the signal path to thefirst node by using the redundant IP router in place of the failed IProuter.
 16. The computer-readable medium having computer-executableinstructions according to claim 15, wherein said transmitting stepfurther includes the optical cross-connect at the second nodetransmitting the request to an optical cross-connect at the first node.17. The computer-readable medium having computer-executable instructionsaccording to claim 13, wherein said transmitting step includes theredundant IP router transmitting the request to an optical cross-connectat the first node to re-establish the signal path by using the redundantIP router in place of the failed IP router.
 18. An IP/Optical Layersystem, comprising: a first IP router at a first node; a second IProuter at a second node that receives a light signal path transmittedfrom said first IP router; an optical network that receives a request tore-establish the light signal path transmitted from said first IProuter, when said first IP router determines that the light signal pathhas failed, and reestablishes the light signal path using a third IProuter in place of said second IP router at the second node.
 19. AnIP/Optical Layer system according to claim 18, wherein the first IProuter determines that the light signal path has failed when the secondIP router fails.
 20. An IP/Optical Layer system according to claim 19,wherein said optical network includes an optical cross-connect at thefirst node, and said optical-cross connect at the first node transmitsthe request to re-establish the light signal path to a cross-connect atthe second node.